Detection of dynamic signals from multiplexed SOA-based fiber-ring laser sensors.

A simple matched filter demodulation configuration for detecting dynamic signals from multiplexed semiconductor optical amplifier (SOA)-based fiber-ring laser sensors is investigated theoretically and experimentally. It is feasible for multiple points fiber Bragg grating sensing because the inhomogeneous broadening of the SOA source makes it possible to produce multimode lasing without mode competition. The best operating points for matched filter demodulation and the wavelength demodulation range are investigated. In the experiment, the simultaneous dual-channel detection of dynamic strains at high frequencies is presented by using piezoelectric transducers. An example application for simultaneous two-channel ultrasonic detection has been successfully demonstrated. The detection system design is simple, low cost, and high precision, making it attractive for applications in structure health monitoring.

Dimalononitrile-containing probe based on aggregation-enhanced emission features for the multi-mode fluorescence detection of volatile amines.

A novel multi-mode probe consisting of a hexaphenyl-1,3-butadiene derivative, 2,2'-((((1Z,3Z)-1,2,3,4-tetraphenylbuta-1,3-diene-1,4-diyl)bis(4,1-phenylene))bis(methanylylidene))dimalononitrile (ZZ-HPB-CN), with typical aggregation-enhanced emission (AEE) features was easily prepared for the highly sensitive and rapid detection of amine vapors. The ZZ-HPB-CN sensor, which was prepared by simply depositing ZZ-HPB-CN on filter paper, could detect low concentration vapors of volatile amines using fluorescence, ultraviolet and naked-eye detection. The limit of detection of the sensor was as low as 1 ppb for the fluorescence detection. The color change of the sensor caused by 1-10 ppm amine vapors could be observed under UV light or with the naked eye. The high sensitivity, quick response and easy operation of the probe give it great potential for real-life applications.

Remote Evaluation of Rotational Velocity Using a Quadrant Photo-Detector and a DSC Algorithm.

This paper presents an approach to remotely evaluate the rotational velocity of a measured object by using a quadrant photo-detector and a differential subtraction correlation (DSC) algorithm. The rotational velocity of a rotating object is determined by two temporal-delay numbers at the minima of two DSCs that are derived from the four output signals of the quadrant photo-detector, and the sign of the calculated rotational velocity directly represents the rotational direction. The DSC algorithm does not require any multiplication operations. Experimental calculations were performed to confirm the proposed evaluation method. The calculated rotational velocity, including its amplitude and direction, showed good agreement with the given one, which had an amplitude error of ~0.3%, and had over 1100 times the efficiency of the traditional cross-correlation method in the case of data number N > 4800. The confirmations have shown that the remote evaluation of rotational velocity can be done without any circular division disk, and that it has much fewer error sources, making it simple, accurate and effective for remotely evaluating rotational velocity.

Fast analyses and designs of long-period fiber grating devices with cosine-class apodizations by using Fourier mode coupling theory.

This paper presents an analytical approach to fast analyzing and designing long-period fiber grating (LPFG) devices with cosine-class apodizations by using the Fourier mode coupling (FMC) theory. The LPFG devices include LPFGs, LPFG-based in-fiber Mach-Zehnder and Michelson interferometers, which are apodized with the cosine-class windows of cosine, raised-cosine, Hamming, and Blackman. The analytic models (AMs) of the apodized LPFG devices are derived from the FMC theory, which are compared with the preferred transfer matrix (TM) method to confirm their efficiencies and accuracies. The AM-based analyses are achieved and verified to be accurate and efficient enough. The AM-based analysis efficiency is improved over 1318 times versus the TM-based one. Based on the analytic models, an analytic design algorithm is proposed and then applied to designing these LPFG devices, which has the complexity of O(N) and is far faster than the existing design methods.

Analytic models of spectral responses of fiber-grating-based interferometers on FMC theory.

In this paper the analytic models (AMs) of the spectral responses of fiber-grating-based interferometers are derived from the Fourier mode coupling (FMC) theory proposed recently. The interferometers include Fabry-Perot cavity, Mach-Zehnder and Michelson interferometers, which are constructed by uniform fiber Bragg gratings and long-period fiber gratings, and also by Gaussian-apodized ones. The calculated spectra based on the analytic models are achieved, and compared with the measured cases and those on the transfer matrix (TM) method. The calculations and comparisons have confirmed that the AM-based spectrum is in excellent agreement with the TM-based one and the measured case, of which the efficiency is improved up to ~2990 times that of the TM method for non-uniform-grating-based in-fiber interferometers.

Analytic solutions for spectral properties of superstructure, Gaussian-apodized and phase shift gratings with short- or long-period.

The analytic solutions (AS) for the spectral properties of short- and long-period waveguide gratings with the effects of discrete phase shift (PS), Gaussian-apodization (GA) and superstructure are presented in this paper, which are derived from the Fourier mode coupling (FMC) theory proposed recently. The spectral properties include the reflectivity of short-period gratings, and the transmission of long-period gratings. The calculated spectra based on the analytic solutions are achieved and compared with measured cases and that on the transfer matrix (TM) method, in the case of changing grating parameters. The AS-based calculation requires the average time of several milliseconds at common PC, and the AS-based efficiency is improved up to ~6700 times the TM-based one. The comparisons have confirmed that the FMC-based analytic solutions are suitable for the real-time and accurate analyses of some non-uniform waveguide gratings.